1. Field of the Invention
The present invention relates to a structural unit and a method of fixing a lens that forms an optical image and a solid state imaging element that photo-electrically converts the optical image into electrical signals, and in particular relates to a structural unit and a method of fixing a lens and a solid state imaging element, which require a relatively high accuracy in fixing of the lens and the solid state imaging element and which require an adjustment in positioning thereof.
2. Discussion of the Background
In image reading apparatuses that read an image as an optical image using a lens and a solid state imaging element such as a CCD (charge-coupled device), the solid state imaging element (hereinafter sometimes referred to as a CCD) must be precisely placed at a position where a line image is formed by the lens. That is, for precisely reading an image with predetermined optical characteristics of the lens (e.g., focusing, magnification characteristics, etc.), precise adjustment of the relative position of the lens and the CCD is required. At the same time, it is necessary to fix each of the lens and the CCD with relatively high accuracy with minimal positional deviation, after adjustment of respective positions of the lens and the CCD.
Conventionally, screws have been used in fixing a CCD and a lens. When screws are used in fixing a CCD and a lens, generally, positional deviation of from several hundreds mm to several tens xcexcm is observed in the position of the CCD relative to the lens.
Japanese Patent Laid-open Publication No. 5-328017 describes a method of using a relatively complicated mechanism including an arrowhead, a ball, a spring, etc., instead of screws. The number of parts of the mechanism is relatively large and consequently the cost of the mechanism is relatively high.
Therefore, recently, a method of using an adhesive agent has been attempted for fixing a CCD and a lens, in which positional deviation with respect to the CCD and the lens and the number of parts used in fixing are relatively small as compared with the method of using screws in fixing the lens and the CCD.
As a method of fixing a CCD and a lens with an adhesive agent, a method referred to as filling bonding is known, as described for example in Japanese Patent Laid-open Publication No. 7-297993.
In the filling bonding method, a gap greater than an adjusting margin for positional adjustment is provided between members to be bonded, and an adhesive agent is filled in the gap so that the members are bonded together with the adhesive agent. In the method, the amount of the gap is set such that the members to be bonded together will not contact each other even when the shapes of the members are varied from the designed shapes. For the adhesive agent, an adhesive material that becomes rigid by ultraviolet light in a short time, about 5 seconds, is used to provide high productivity.
However, the volume contraction percentage of an adhesive agent that becomes rigid by ultraviolet light when the adhesive agent becomes rigid is generally about from 5% to 10%. If the volume contraction percentage is 7%, when the shape of the hardened adhesive agent is a cube, the cube-shaped adhesive agent contracts about 2% in each of the three-dimensional directions thereof. Accordingly, in the filling bonding method, when the thickness of the adhesive agent for bonding members to be bonded together is relatively large, for example, about 1 mm, contraction of about 2%, i.e., a positional deviation of about 20 xcexcm, occurs in each of the three dimensional directions. This contraction causes a positional deviation in the members to be bonded together when the members are fixed. Thus, the filling bonding method cannot be applied in fixing a CCD and a lens in a CCD lens unit that requires a relatively high accuracy, e.g., a positional deviation of about 20 xcexcm or smaller, in fixing the CCD and the lens.
Japanese Patent Laid-open Publication No. 10-309801 describes a method that realizes a relatively high accuracy in fixing members using an adhesive agent. JP No. 10-309801 relates to a structure to mount an ink jet printing head to a head supporting member with high accuracy. In the mounting structure, an intermediary mounting member is arranged between the ink jet printing head and the head supporting member, and the intermediary supporting member is fixed to the ink jet printing head by an adhesive agent, and at the same time, to the head supporting member as well via the adhesive agent.
In the above-described structure, the volume contraction of an adhesive agent occurring when the adhesive agent is hardened is converted only to a movement of the intermediary support member to be attached by the adhesive agent, so that positional deviation in other parts, e.g., in the ink jet printing head, is avoided.
The applicant of the present invention has previously proposed to apply the above-described structure of JP No. 10-309801 to a CCD lens unit including a CCD and a lens, in which the CCD and a CCD supporting member are bonded together via an intermediary supporting member. The number of parts in the proposed CCD lens unit is small as compared with the mechanism of JP No. 5-328017 including an arrowhead, etc. However, besides the CCD and the lens, parts for supporting or fixing the CCD and the lens are still needed, such as the intermediary supporting member for supporting the CCD, a lens housing tube for housing and supporting the lens and a pressing plate for fixing the tube, and a supporting member for supporting the intermediary supporting member and the lens housing tube.
The present invention has been made in view of the above-discussed and other problems and addresses the above-discussed and other problems.
Preferred embodiments of the present invention provide a novel structural unit and a method for fixing a solid state imaging element and a lens, which realize a relatively high accuracy in fixing the solid state imaging element and the lens and at the same time realizes a significant reduction in the number of parts used in fixing the solid state imaging element and the lens.
Other preferred embodiments of the present invention provide a structural unit for fixing a solid state imaging element and a lens, in which the positional adjustment with respect to the solid state imaging element and the lens can be performed in 5 axial directions.
According to a preferred embodiment of the present invention, a structural unit includes a lens that forms an optical image, a solid state imaging element placed in a predetermined position relative to the lens, and an intermediary supporting member that may be bonded and fixed to each of the lens and the solid state imaging element by an adhesive so that the lens and the solid state imaging element are integrated with each other in a state that a positional relation between the lens and the solid state imaging element is maintained. In this configuration, because the intermediary supporting member is bonded and fixed to each of the lens and the solid state imaging element by the adhesive so that the lens and the solid state imaging element are integrated with each other in a state that a positional relation between the lens and the solid state imaging element is maintained, the effect of contracting of the adhesive when the adhesive is hardened is absorbed by the movement of the intermediary member, so that the lens and the solid state imaging element are fixed with relatively high accuracy. Further, by bonding each of the lens and the solid state imaging element to the intermediary supporting member, various parts that are generally required for fixing the solid state imaging element and the lens, e.g., a lens supporting member, a lens housing tube, a lens pressing plate, and screws for fastening the pressing plate, etc., which are used in some background structural units, are not required.
The unit may further include a mounting part provided to one of the lens and the solid state imaging element and configured to mount the unit to an apparatus. The mounting part may be configured to function as a reference for mounting the unit to the apparatus.
In the above-described unit, each bonding surface of the lens, the solid state imaging element, and the intermediary supporting member may be flat.
Further, the bonding surface of the lens may be in parallel to an optical axis of the lens, and the bonding surface of the solid state imaging element may be perpendicular to the optical axis of the lens. In this configuration, by sliding the bonding surface of the lens, the positional adjustments for the lens and the solid state imaging element can be performed in three directions, i.e., the x-coordinate direction (the main scanning direction), the z-coordinate direction (the optical axis direction), and the xcex3 direction (the rotation direction around the z-coordinate). Similarly, by sliding the bonding surface of the solid state imaging element, the positional adjustments for the lens and the solid state imaging element can be performed in three directions, i.e., the x-coordinate direction (the main scanning direction), the y-coordinate direction (the sub-scanning direction), and the xcex2 direction (the rotational direction around the z-coordinate). Thus, in this configuration, the positional adjustments for the lens and the solid state imaging lens can be performed in 5 axial directions.
Furthermore, the adhesive may be an adhesive that becomes rigid in response to ultraviolet light. Because the hardening time of such an adhesive is relatively short, the time required for producing the structural unit can be reduced.
Still further, the intermediary supporting member may be made of a material that passes the ultraviolet light. This configuration allows the adhesive arranged between the intermediary supporting member and the lens and the solid state imaging element to be uniformly, quickly, and efficiently hardened.
Furthermore, the mounting part provided to the lens may include a parallel mounting plane that is in parallel with the optical axis of the lens, a perpendicular mounting plane that is perpendicular to the optical axis, and a mounting plane that is perpendicular to both of the parallel mounting plane and the perpendicular mounting plane. This configuration enables positioning of the structural unit in three axial directions and thereby positioning the structural unit relative to the mounting apparatus.
Still furthermore, the mounting part provided to the lens may include a mounting plane that is parallel with the bonding surface of the lens and a through hole perpendicularly passing through the bonding surface of the lens and the mounting plane of the mounting part that is parallel with the bonding surface. This configuration allows the lens to be used as a reference in mounting the structural unit in an apparatus.
According to another preferred embodiment of the present invention, a method of fixing a lens and a solid state imaging element to be placed in a predetermined position relative to the lens includes the steps of individually grasping the lens and the solid state imaging element and positioning the solid state imaging element in the predetermined position relative to the lens. Hardening adhesives are placed between each bonding surface of the lens and the solid state imaging element and a bonding surface of an intermediary supporting member that is in a free condition in a state that the solid state imaging element and the lens are maintained in respective positions after the solid state imaging element has been positioned in the predetermined position relative to the lens. The intermediary supporting member in the free condition is supported by respective surface tensions of the adhesives placed between the bonding surfaces of the lens, the solid state imaging lens, and the intermediary supporting member.
The method may further include the step of providing a mounting part for mounting the lens and the solid state imaging element to an apparatus to one of the lens and the solid state imaging element.
Further, the method may include the step of forming each of bonding surfaces of the lens, the solid state imaging element, and the intermediary supporting member to be flat.
Furthermore, the method may further include the step of placing the bonding surface of the lens in parallel to an optical axis of the lens, and placing the bonding surface of the solid state imaging element perpendicular to the optical axis of the lens.
Still furthermore, in the method, the step of hardening the adhesives may include the step of using an adhesive that becomes rigid in response to ultraviolet light. Further, the step of hardening the adhesives may include the step of using an intermediary supporting member that passes ultraviolet light.
Furthermore, the mounting part providing step may further include the step of providing the mounting part to the lens, wherein the mounting part may include a parallel mounting plane in parallel with the optical axis of the lens, a perpendicular mounting plane perpendicular to the optical axis, and a mounting plane perpendicular to both of the parallel mounting plane and the perpendicular mounting plane. The mounting part may further include a mounting plane parallel with the bonding surface of the lens, and a through hole that perpendicularly passes through the bonding surface of the lens and the mounting plane of the mounting part in parallel with the bonding surface of the lens.